Halophilic CO₂-fixing microbial community as biocatalyst improves the energy efficiency of the microbial...

Using saline electrolytes in combination with halophilic CO₂-fixing lithotrophic microbial catalysts has been envisioned as a promising strategy to develop an energy-efficient microbial electrosynthesis (MES) process for CO₂ utilization. Here, an enriched marine CO₂-fixing lithotrophic microbial community dominated by Vibrio and Clostridium spp. was tested for MES of organic acids from CO₂. At an applied E_cathode of -1V (vs Ag/AgCl) with 3.5 % salinity (78 mScm^-1), it produced 379 ± 53 mg/L (6.31 ± 0.89 mM) acetic acid and 187 ± 43 mg/L (4.05 ± 0.94 mM) formic acid at 2.1 ± 0.30 and 1.35 ± 0.31 mM day^-1, respectively production rates. Most electrons were recovered in acetate (68.3 ± 3 %), formate (9.6 ± 1.2 %) besides hydrogen (11 ± 1.4 %) and biomass (8.9 ± 1.65 %). Notably, the bioproduction of organic acids occurred at a high energetic efficiency (EE) of ∼ 46 % and low E_cell of 2.3 V in saline conditions compared to the commonly used non-saline electrolytes (0.5-1 mScm^-1) in the reported MES studies with CO₂ (E_cell: >2.5 V and EE: <34 %).